Among 12 recombinant inbred (RI) mouse strains derived from crossing C57BL/6J and C3H/HeJ mice, one strain, designated BXH-2, spontaneously expresses a B-ecotropic MuLV throughout life and has a high incidence of myeloid leukemia. Virtually 100% of BXH-2 mice die of leukemia of myeloid origin by a year of age. BXH-2 mice represent one of the few inbred strains that have a high incidence of myeloid leukemia. In fact, BXH-2 mice have the highest spontaneous myeloid tumor incidence of any inbred strain yet identified. Southern analysis using a highly specific ecotropic MuL V DNA-derived probe indicated that 125 of these tumors contained newly acquired tumor-specific provirus and 25 of these tumors contained only a single tumor-specific provirus. To identify the genes that are activated by viral integration in BXH-2 myeloid tumors we have molecularly cloned somatically acquired proviruses along with cellular flanking sequences. We have identified a common viral integration site, designated Evi-4, in a BXH-2 myeloid tumor that may represent a novel cellular proto-oncogene involved in murine hematopoietic disease. By use of an interspecific hybrid mouse mapping panel Evi-4 was mapped to mouse chromosome 2 and appears to be a novel locus involved in murine myeloid leukemogenesis. Specifically utilizing BXH-RI mice we propose to: (1) determine the location and orientation of proviruses within the Evi-4 locus; (2) identify transcripts from Evi-4 expression; (3) identify the protein product of the Evi-4 gene and establish its role in normal development and leukemogenesis; and (4) generate transgenic mice to investigate the effects of Evi-4 activation on growth control and differentiation.